As an engineering student going into fluid dynamics next semester this is very relevant to me. The mathematics of a surfboards design has always intrigued me

Thanks for answering my question in so much detail! Love the explanations here, will be looking for some bigger fins soon, can't wait to try it 👌 indeed have been in situations where I felt the back just slided away. Especially on steeper wave faces

Finally know why people prefer large fin regardless of their weights are, very inspiring!

Best Surf Channel on the planet !!!!!

Hi Harry, I've been watching a lot of Noel Salas (surf n show youtube channel) board reviews and when he talks about fin sizes he explains that he likes a large fin in small surf because it gives him some more surface to push off of and generate speed, however when the waves get bigger the large fins give too much lift at these higher speeds so he opts for a medium fin in bigger surf. Just wanted to share that info, we're all here to learn from each other. I do like the theory of going for a large fin as beginner intermediates (they wont put themselves in waves where they get too much lift anyway) and the extra stability will definitely help

Love these videos, also the way you use different coloured markers to help illustrate.

Thanks for the video! I now know I bought the wrong size fins! :( However, when I was looking to buy fins I was also really confused about the different type of materials. Specifically, when looking at the FCS brand. Can you provide some insight into what material you should consider for the Level II / Level III range? Thank you!

Can you chat about the effects of bonzer set ups? With the fin differences (5 and 3) and the larger concaves/cant

Nice vid! could u talk about the right paddle positioning in shortboards and longboards?

love your channel! you earned a new subscriber! keep up the good work !

These videos are amazing. Thank you guys so much for all the knowledge!

Thank you for that video and all the good work you are putting in your videos, i really appreciate them!! I am currently shaping an EPS board and hope that it'll float a bit better than i am used to on my PU boards, and i am not really getting your calculation at the end. While we are standing and surfing the board, i totally agree with what you are saying. But if we are paddling it's a different thing i believe. The density of our bodies is similar to the density of water and if we use our techniques to swim we float at the surface. If we now have a surfboard to paddle on, the lightest foam can provide an extra 30% force to move us out the water, doesn't it? Cheers, looking forward for your answer

great work as usual!

Great video! Would be interesting to accuratly measure the amount of drag (speed-loss) with bigger fins in comparison to smaller ones, similar to the tail-rocker calculation you mention in the beginning of the video. Also the amount of drag with different fin setups (thruster vs quad vs twin etc) - would be awesome to get some scientific data and the physics behind it.

I’ve always heard that channel bottoms you need a smaller fin because each channel acts like a mini fin. I’ve also heard that larger fins create more lift and catch more in choppy waves for smaller surfers. I’ve also heard larger fins create more drag making you slow down and not make sections and also can extend the radius of a turn making it more drawn out and less tight. Are any of these true?? I surf primarily a top to bottom quick walled/closed out beach break so it’s imperative unless it’s pumping for me to do quick radius turns and to be able to make it down the line and to the lip quicker that’s why I ride mediums and even smalls at times. I also ride larges in bigger surf mainly just wondering what all you can tell me about all this just looking for information thanks Harry!

How do you put it all together to pick a board?

great video as usual ! what do you recommend more as summer (1-3ft waves)board short fat groveller like firewire twice baked or longer thinner minimal like seaside and beyond in same volume let say around 40liters surfer is intermediate level ?

The whole weight difference thing is more affected by winter wetsuit, boots, gloves, all water saturated, Versus tropical surfing in boardshorts and maybe a rash vest for sun protection than the foam of the board. Cheers for the knowledge on fins!

What about wave size? you mentioned that Kristin Moore uses large fins but the wave size she rides will tend to be a bit larger giving her more room to make her turns. I tend to ride smaller waves and I am about her weight would that not slow down my turns on a smaller faced wave? Thank you for your videos.

There is a lot of debate about flex in a board. I have heard flex helps and that stiffness helps. I have been riding mostly polyester boards most of my life with only a handful of my boards being epoxy, so my experiance between the difference is zilch. Is there mathematical explanation between the two? I do know that there is a huge difference when it comes to long boarding, but I primarily short board, so I haven't dabled in it too much. Thanks for the vids.

Always great content! Have a look to a company called Notox. The boards are EPS with epoxy resin but uses flax instead of fiberglass, and are vacuum bagging their boards which they say is using less resin and they feel also lighter. Also the feeling is closer to a PU. Why this would come from?

can you do epoly vs PU/PE, EPS/EPOXY just not to many shapers use the epoly combination (epoxy polyurethane board) and it seems odd because they make perfect sense strong because of the epoxy and flexible because of the polyuretane that way when the condition get choppier you can still have a great surf, it just seems in every sense the best combination.

You talked about the effects of lots of exit rocker, would the same thing apply if there was lots of entry rocker?

What happened to the hydro foil fins I don't see them around anymore

I think the horizontal component of the force on the tail will only be that big on dead flat water. In practice you put your tail in the steaper part of the face.

Where can I find the diagram on the whiteboard?

Trying to find one of your videos where you explain that 'impressive' flow chart on the wall!... ? I also am having a giggle to myself given the name of your channel 'Surf Simply', and the rather not so simplicity of your said flow chart ;) hehe Its great your putting effort into providing these videos in a quite scientific way... Maybe channel could be called Surf Scientific 😉

Is EPS/Epoxy more ding-resistant? As a newbie, want to get a board that's more durable.

can we see that level map closer ...if it is cool could you sell it as a poster , I would buy it.

👏

i really like you're crushing a bit that dogma about eps buoyancy.

Force is measured in Newtons or pounds. Not kg.

Totally agree with you on fin sizing. I've developed a set of xxl fins for heavier surfers. They will be available at Bigguyboards.com in one or two weeks

I feel that you are oversimplifying some of the PU vs. EPS facts and fiction. If we go back to when EPS was starting to be explored for high performance boards then anyone who cared about their board or had a strong opinion about having a high performance board was probably riding ultra light blank with 4oz + 4oz 3/4 on the deck and 4oz on the bottom. My PU Clark foam boards with their FCS 1 plugs were in the 4 pound range without wax/fins/stomp pad. 5'11" x 18.5" at about 25-27L. Now my EPS boards are weighing 5-6 pounds. You want to ignore the fact that 1 Kg in board doesn't matter because you weigh 80Kg. All your weight is not on the board consistently if you are pumping down the line or doing an air all or most or you weight will come off the board. I am willing to ignore that fact and want to discuss the hypothetical PU vs EPS that this video was about. If I had two boards with identical shape and volume (assuming shaper will change thickness of blank to deal with thickness of S-cloth / epoxy ...) then the biggest difference would be the distribution of weight in my opinion. If EPS is lighter than PU foam then the weight of the two boards of equal weight would come from the glass / resin. If more weight comes from foam/volume then that means more weight is under my front foot where the volume is and less weight is as the nose / tail proportionately . If you want to spin the board around then the higher weight in the nose on an EPS would be a hinderance. Every wave is different and ever board is different and humans and their perceptions change over time, but I still have some old under volume Clark foam boards with team rider glass that have some qualities that my right sized EPS boards do not have.

I'm 106 kilo where is my xxl fin!!! lol